The present invention relates to cardiac pacing generally and in particular to a cardiac pacemaker which regulates pacing rate based upon sensed percentage of oxygen saturation of the blood.
The relationship between oxygen saturation of the blood and pulse rate in a healthy heart is well known. This relationship has given rise to numerous proposals for pacemakers which regulate pacing rate in response to sensed blood oxygen level. These pacemakers attempt to restore the natural relationship between blood oxygen level and pulse rate in order to provide a pacemaker which paces the heart at a rate appropriate to the physiological demands of the patient's body.
An early proposal for such a pacemaker is set forth in U.S. Pat. No. 4,202,339, issued to Wirtzfeld et al. This pacemaker takes the form of an asynchronous pacemaker which does not sense the heart's underlying electrical activity. U.S. Pat. No. 4,467,807, issued to Bornzin and incorporated herein by reference in its entirety discloses a pacemaker in which the oxygen sensor's function is integrated with a sense amplifier for sensing intrinsic heart activity. This approach is believed superior to that of Wirtzfeld in that it avoids competing with underlying heart activity and allows the heart to beat at its own, underlying rhythm if that underlying rhythm is appropriate.